The introduction of HDTV (high definition television) receivers has been accompanied by requests for recording of HDTV videos for use by a present video cassette recorders. At the same time, it has been desirable to maintain high resolution, one of features of the HDTV. In response to multi-image processing, it is anticipated that demand will be boosted for recording videos by various broadcasting systems, such as present NTSC-encoded, etc., Hi-Vision, and a digital broadcasting system simultaneously in high resolution format. In order to realize these functions, for instance, when a Hi-Vision signal must be converted into a NTSC-encoded signal, the Hi-Vision signal transmitted on a MUSE (Multiple sub-Nyquist Sampling Encoding system) signal must be converted into the NTSC-encoded signal.
A conventional scanning-line-converter comprises a MUSE-NTSC converting circuit as described in the unexamined Japanese Patent Application publication No. H07-123372. The conventional converter employing the MUSE-NTSC converting circuit is described here by referring to FIG. 16, which is a block diagram depicting a conventional video signal converter.
An operation of an A/D (Analog to Digital) converter 200 is described as follows: A MUSE input signal converted from analog to digital by the A/D converter 200 is fed into a MUSE input process circuit 201 as well as a MUSE synchronous signal (hereinafter called "sync signal") generating circuit 202. Based on a MUSE sync signal tapped off from the MUSE sync signal generating circuit 202, a MUSE timing signal generating circuit 203 taps off a MUSE timing signal. Based on the MUSE sync signal and the MUSE timing signal, a MUSE input process circuit 201 taps off a digital video signal which has undergone an input process. The digital video signal is written into a MUSE-NTSC converting RAM 205. A NTSC timing signal generating circuit 207 receives a NTSC-encoded clock signal tapped off from a NTSC clock signal generating circuit 208, and produces a NTSC-encoded timing signal. A NTSC-encoded MUSE signal is read out from the MUSE-NTSC converting RAM 205 using the NTSC-encoded timing signal, and fed into a MUSE summary decoding circuit 206. A video signal, which is decoded into a NTSC signal tapped off from the MUSE summary decoding circuit 206, is fed into an output process circuit 209, whereby a NTSC output signal is obtained. The NTSC-encoded timing signal generating circuit 207 produces a sync signal for the NTSC output signal.
According to the above operation, however the MUSE summary decoding circuit exclusively used for NTSC conversion is used for the conversion from MUSE signal to NTSC signal. Because of a simplified circuit in the MUSE summary decoding circuit, the NTSC-encoded output signal by the summary MUSE decoding circuit shows a deteriorated video both in horizontal and vertical directions compared with that shown by HDTV base band output signal obtained by decoding a MUSE signal correctly.
When both of the HDTV base band output signal and the NTSC output signal can be obtained simultaneously in response to the MUSE input signal, the summary MUSE decoding circuit is used in addition to a decoding circuit of the MUSE signal. Therefore, the above operation uses a complicated as well as a large-sized circuit.